ccsds_encoder_impl.cc

/* -*- c++ -*- */
/*
 * Copyright 2014 Free Software Foundation, Inc.
 *
 * This file is part of GNU Radio
 *
 * SPDX-License-Identifier: GPL-3.0-or-later
 *
 */

#ifdef HAVE_CONFIG_H
#include "config.h"
#endif

#include "ccsds_encoder_impl.h"
#include <gnuradio/fec/generic_encoder.h>
#include <cstdio>

#include <gnuradio/fec/viterbi.h>

namespace gr {
namespace fec {
namespace code {

generic_encoder::sptr ccsds_encoder::make(int frame_size, int start_state, cc_mode_t mode)
{
    return generic_encoder::sptr(new ccsds_encoder_impl(frame_size, start_state, mode));
}

ccsds_encoder_impl::ccsds_encoder_impl(int frame_size, int start_state, cc_mode_t mode)
    : generic_encoder("ccsds_encoder"),
      d_start_state(static_cast<unsigned char>(start_state)),
      d_mode(mode)
{
    d_max_frame_size = frame_size;
    set_frame_size(frame_size);
}

ccsds_encoder_impl::~ccsds_encoder_impl() {}

int ccsds_encoder_impl::get_output_size() { return d_output_size; }

int ccsds_encoder_impl::get_input_size()
{
    return d_frame_size / 8; // packed byte input
}

const char* ccsds_encoder_impl::get_input_conversion()
{
    // Expects packed data input; tell wrapper to pack it.
    return "pack";
}

bool ccsds_encoder_impl::set_frame_size(unsigned int frame_size)
{
    bool ret = true;
    if (frame_size > d_max_frame_size) {
        GR_LOG_INFO(d_logger,
                    boost::format("tried to set frame to %1%; max possible is %2%") %
                        frame_size % d_max_frame_size);
        frame_size = d_max_frame_size;
        ret = false;
    }

    d_frame_size = frame_size;

    if (d_mode == CC_TERMINATED) {
        d_output_size = 2 * (d_frame_size + 7 - 1);
    } else {
        d_output_size = 2 * d_frame_size;
    }

    return ret;
}

double ccsds_encoder_impl::rate() { return 0.5; }

void ccsds_encoder_impl::generic_work(void* in_buffer, void* out_buffer)
{
    unsigned char* in = (unsigned char*)in_buffer;
    unsigned char* out = (unsigned char*)out_buffer;

    unsigned char my_state = d_start_state;

    if (d_mode == CC_TAILBITING) {
        // Grab K-1 (6) bits of data from the last input byte to add
        // onto the from of the encoding stream for tailbiting mode.
        unsigned char sym = in[d_frame_size / 8 - 1];
        for (unsigned int i = 0; i < 7 - 1; ++i) {
            my_state = (my_state << 1) | ((sym >> (5 - i)) & 1);
        }
    }

    my_state = encode(out, in, d_frame_size / 8, my_state);

    if (d_mode == CC_TERMINATED) {
        // encode works on bytes, but we are only adding some number
        // of bits to the end of the frame, so we abuse the encode
        // function by reshifting the start state within the
        // for-loop and only taking the last two bits out of the
        // encoded 2-bytes.
        unsigned char end_bits[16];
        for (unsigned int i = 0; i < (7 - 1); ++i) {
            my_state = (my_state << 1) | ((d_start_state >> (7 - 2 - i)) & 1);
            encode(&end_bits[0], &my_state, 1, my_state);
            out[(i + d_frame_size) * 2 + 0] = end_bits[14];
            out[(i + d_frame_size) * 2 + 1] = end_bits[15];
        }
    }

    if (d_mode == CC_TRUNCATED) {
        my_state = d_start_state;
    }

    d_start_state = my_state;
}

} /* namespace code */
} /* namespace fec */
} /* namespace gr */